ABSTRACT Smoking is the leading cause of preventable death and disability in the U.S., and is becoming increasingly concentrated among individuals with low socioeconomic status (SES) and racial/ethnic minorities. Nearly half of U.S. adults have difficulties with health literacy (HL), and lack the ability to obtain, understand, and use basic health information to make important decisions about healthcare. As with smoking, low HL is common among racial/ethnic minorities and those with low SES. Low HL is associated with negative health behaviors, less engagement in preventive services, and poor health outcomes. It is also associated with current smoking, key established predictors of smoking relapse, and smoking relapse, even after controlling for sociodemographic indicators. Thus, low HL appears to be an independent risk factor for poor cessation outcomes among low- SES, racially/ethnically diverse smokers. Efforts are needed to elucidate mechanisms of the association between low HL and relapse, and to develop smoking cessation interventions targeting low HL smokers. This project aims to: 1) investigate mechanisms through which HL influences smoking cessation in low- SES, racially/ethnically diverse smokers enrolled in cessation treatment using secondary analyses of traditional questionnaire and ecological momentary assessment (EMA) data from 2 smoking cessation treatment studies; 2) conduct a qualitative investigation with low HL smokers to further elucidate mechanisms of the association between HL and cessation and inform the development of a theoretically-based, cessation treatment targeting the specific needs of low HL smokers; 3) develop and evaluate the preliminary efficacy of a smoking cessation intervention targeting low HL smokers compared to standard treatment; and 4) examine treatment effects on secondary outcomes of interest (e.g., differential dropout, treatment satisfaction, intention to quit smoking). Results will elucidate the complex relations between HL and cessation in underserved smokers, guide treatment for low HL smokers, and contribute to reducing tobacco-related health disparities. Diana Stewart Hoover, Ph.D. is seeking 5 years of support through a NIDA K23 Career Development Award for the proposed training and research. In order to fill critical gaps in her experience, she will obtain specialized training in behavioral intervention development targeting underserved populations, advanced statistics for analyzing longitudinal and EMA data, and qualitative methods, particularly mixed methods. She will also expand her knowledge and skills related to HL, tobacco cessation, health disparities, and research ethics. Her training and research plans will support her long-term goal of establishing an independently-funded research program in cancer prevention and tobacco cessation, with a focus on reducing tobacco-related health disparities for individuals with low HL. A comprehensive training plan is described, combining mentored research, structured mentorship activities guided by established researchers in the field, formal coursework and workshops, and participation in seminars at the University of Texas MD Anderson Cancer Center.